The long term goal of this proposal is to unravel hormonal-regulated changes of ion channel expression and function in uterine smooth muscle, with special emphasis on Ca2+ dependent K+ channels (MaxiK), fast transient K+ channels (Kv4.3, ITO) and L-type Ca2+ channels. The main hypothesis is that during pregnancy differential expression of K+ and Ca2+ channel types, isoforms, and regulatory subunits contribute to the dramatic changes that occur in uterine excitability and contractility. Our preliminary data show that: 1) Expression of the MaxiK channel alpha subunit, the Kv4.3 K+ channel (ITO), and the Ca2+ channel alpha1C and beta2a subunits, varies during pregnancy; 2) RNAse protection assay (RPA) shows that the reduction in protein expression of MaxiK alpha subunit and Kv4.3 channels correlates with changes in mRNA levels; 3) Blockade of Kv4.3 channels enhances contractility; 4) A novel splice insert of the Maxi K alpha subunit may act as a dominant negative expression regulator; 5) Reduction in the expression level, at the end of pregnancy, of MaxiK and Kv4.3 channels may be associated with altered trafficking, and 6) Myometrium from non-pregnant rats primed with beta-estradiol have reduced Kv4.3 channel expression. Thus, the questions to answer are: a) What are the physiological and pharmacological changes that MaxiK channels undergo during pregnancy? b) Which splice variants of MaxiK alpha subunit are present in myometrium and what is their functional impact? c) What is the molecular nature of ITO currents in myometrium? d) What is the role of ITO currents in myometrial contractility? e) What are the molecular components of L-type Ca2+ channels (alpha1C and beta subunits), and are they differentially expressed during pregnancy? f) What are the functional properties of L-type Ca2+ currents at different stages of pregnancy? g) Which is the mechanism(s) responsible for the changes in expression levels of K+ and Ca2+ channels, and which sex hormone(s) controls channel expression? The Specific Aims will use a multidisciplinary approach to investigate at different stages of pregnancy and with hormonal treatment: 1) changes in function, protein expression and mRNA levels of the MaxiK channel, 2) which MaxiK alpha subunit splice variants are present in myometrium, their functional properties, and their expression, 3) the molecular nature and function of fast transients K+ currents, and 4) the nature and changes in alpha1C Ca2+ channels and regulatory beta subunits. These studies will be relevant to design or improve therapeutic treatment(s) for pathological situations such as premature labor and dysmenorrhea.